You’ve long since figured this out, but here’s a version for those who haven’t.
Create a stack of buttons. Select them all, go to the Elements inspector and assign them the same background color. Click in the center of the grid in the border area, set the radius to zero and hit the down arrow in the Width field to set the stroke width to zero. Click on the bottom center of the grid and click on the Width up arrow and click in the color well to give it a contrasting color.
Arrange the buttons so that the top and bottom edges align. Make sure not to overlap the bottom strokes. Select them all and use the Arrange menu to group them. Move the group so that the bottom edge is around 1 pixel higher than the bottom edge of the header / menu bar. Make sure that the button group is behind the header / menu bar.
Click on the field at the left of the timeline where it says “Main Timeline”. Select “New Timeline” from the pop-up and name it “Menu1 Timeline” or something similar. This will create the new timeline and take you there.
Make sure the time cursor is at the start, then select the button group and create a Origin (Top) keyframe (the diamond-plus icon). Drag the time cursor to the 1 second mark and create a second keyframe. Drag the button group down to the desired position.
Go back to the Main timeline. You will notice that the button group is back where it started. Now create a button on the menu bar to summon that menu. Select the button and go to the Actions inspector, select On Mouse-Up > Start Timeline > Menu1 Timeline (or whatever you called the new timeline).
Now click on the preview icon and test it out. When you click on the button it triggers the Menu 1 timeline.
Duplicate this as many times as you need, using a different timeline for each menu.
Note that if you leave that scene and return later, everything is reset.